Comparative kinetics, equilibrium, thermodynamic and mechanistic studies on biosorption of hexavalent chromium by live and heat killed biomass of Acinetobacter junii VITSUKMW2, an indigenous chromite mine isolate

Abstract

The current study focuses on the quantification and mechanistics of Cr(VI) biosorption with Acinetobacter junii, indigenous bacteria isolated from chromite mine sites of Sukinda valley, Orissa, India. The equilibrium sorption capacity 22.22, 13.88, 6.94mg of Cr(VI)g−1 of biomass was obtained for logarithmic phase, stationary phase and heat killed biomass respectively at optimum sorption conditions (pH: 2.0, contact time: 120min, temperature: 27°C, initial Cr(VI) concentration: 100mgL−1, biosorbent dosage: 2gL−1). The Langmuir isotherm model and pseudo first order (Lagergren kinetic model) were observed to hold good for the bio-sorbents. Three subsequent sorption/desorption cycles yielded 54.9, 38.4 and 34.5% regeneration of the biosorbent indicating an irreversible chromium(VI) binding property of the sorbent system. The mechanistic aspects of sorption by heat killed and log phase biomass were compared using FTIR and SEM techniques. The number of binding sites on biomass surface measured by acid/base titration (215μmolg−1 and 99μmolg−1 for logarithmic phase and heat killed biomass respectively) corroborated with the observations made by batch sorption studies. Detailed surface characterization studied through FT-IR, SEM, EDX and zeta potential measurement provided evidence for sorption through oxyanionic binding to the cell surface. The EPR spectroscopy revealed the reduction of Cr(VI) to Cr(V) on the biomass surface upon Cr(VI) sorption.